This proposed work aims to conduct a survey of important stem diseases and insect pests affecting soybean, identifying pests and assessing adopted management practices.
Proposal description – This proposed work aims to conduct a survey of important diseases and insects affecting soybean stems, identifying pathogens, and assessing adopted management practices. Stem diseases of soybean, including anthracnose stem blight, brown stem rot, charcoal rot, Phytophthora stem rot, stem blight, red crown rot, and stem canker, can cause significant loss in yield. According to disease loss estimates reported through the Crop Protection Network (https://cropprotectionnetwork.org/resources/publications/soybean-disease-loss-estimates-2018), stem diseases resulted in 257 million bushels lost. Moreover, in some instances, new diseases have been reported in some soybean production areas, or the identity of the specific pathogens that cause a particular stem disease is not resolved or is changing. For instance, Calonectria ilicicola, the pathogen that causes red crown rot was first identified in Illinois in 2018. 20-30 bu/a losses have been reported when the disease is severe. In a survey conducted in 2020, red crown rot was confirmed in 4 counties in Illinois, including St. Clair, Madison, Pike, and Sangamon (N. Kleczewski personal observation).
Stem canker is another problematic disease that affects yield in soybean. The estimated cumulative economic loss (1996 – 2016) attributed to stem canker in IL is $249 million (Bandara et al., 2020). Northern stem canker is caused by Diaporthe caulivora, while southern stem canker is caused Diaporthe aspalathi. The distribution of either pathogen in Illinois has not been entirely resolved. Moreover, both pathogens are part of the Diaporthe disease complex that also cause seed decay and stem and pod blight on soybean. Besides these two species, there are other Diaporthe species that cause stem canker, although their occurrence in Illinois is not known.
Brown stem rot, another disease affecting soybean stems, is believed to be widespread in Illinois from the central to the northern border. The symptoms and the extent of yield reduction in soybean due to brown stem rot depend on environmental conditions, the cultivar used, and the pathogen type. The reduction in number and size of seeds produced by infected plants may cause yield losses up to 30%. Yield reductions are greatest when wet and cool conditions prevail during the pod-fill stage, followed by hot, dry conditions. Two major subspecific types of the brown stem rot pathogen (Cadophora gregata) are known in the state that cause different symptom patterns, including one pattern that looks similar to the foliar phase of sudden death syndrome; both types can reduce yield. The occurrence of brown stem rot may be less frequent in central and southern Illinois, although the disease is known to occur in Georgia. The distribution throughout the state is not well documented.
Charcoal rot is another disease that affects soybean production across soybean production areas in the United States. Although the disease caused by the fungal pathogen Macrophomina phaseolina has historically been described as a “southern disease”, mainly associated with high temperatures and dry conditions, charcoal rot has been reported to cause losses in the Midwest and in Ontario, Canada. The wide host range of the pathogen and the limited resistance available in northern soybean cultivars stress the need to have a better assessment of the incidence of the disease in Illinois, the extent of yield loss in causes, the diversity in the population of the pathogen across the state, and the producers’ perceptions about the disease.
White mold (Sclerotinia stem rot) caused by the fungus Sclerotinia sclerotiorum is especially problematic in Northern production areas, as the disease is often associated with cool and wet conditions. The disease is characterized by the fluffy white growth of mycelia, often accompanied by the presence of black structures called sclerotia.
Several insects impact soybean production. We are proposing to investigate the impact of Dectes stem borer and the early detection of soybean gall midge on soybean production in Illinois.
Soybean farmers in southern Illinois have noted increased Dectes stem borer (Dectes texanus texanus) damage in recent years. Dectes stem borer larvae bore into the soybean stem; this injury can lead to lodging and, ultimately, yield loss when these larvae girdle the base of the stems as plants mature. The location of Dectes stem borer larvae within the stem makes scouting difficult, and they are often present in fields without causing lodging or yield loss. Furthermore, many factors not related to insect damage can also lead to soybean lodging at harvest time. As a result, the true extent of Dectes stem borer incidence and economic damage is poorly understood in Illinois.
Soybean gall midge (Resseliella maxima) is a new pest of soybean that has caused severe damage in eastern Nebraska and western Iowa. So far, this insect has been detected in five states, but not in Illinois (https://soybeangallmidge.org/soybean-gall-midge-distribution). A similar species was found feeding on white mold in Minnesota but did not cause damage to soybean. Early identification of soybean gall midge if and when it arrives in Illinois will be critical to developing management guidelines for this potential invasive pest. In addition, understanding the distribution of similar, non-damaging gall midge species (which have not been studied in Illinois) will help us avoid “false positive” reports that could distort the true impact of soybean gall midge